Stormwater Inundation Analysis in Small and Medium Cities for the Climate Change Using EPA-SWMM and HDM-2D

The increase of rainfall intensity and flash-flood due to climate change are expected to exacerbate flood inundation in urban area. Especially, small and medium cities lacking drainage facilities are more vulnerable to flood inundation than large cities. This study introduces a simplified urban stormwater inundation simulation modelling for the two small and medium-sized cities located in South Korea using the U.S. Environmental Protection Agency (EPA) Storm Water Management Model (SWMM) and a HydroDynamic Model-2D(HDM-2D). EPA-SWMM model which are widely used to the runoff analysis of urban areas containing drainage pipe network, was used to calculate runoff flow and surcharged overflow of the existing urban drainage network. Then, a 2-D inundation model, HDM-2D was coupled with 1-D EPA-SWMM model to simulate the flood propagation in urban areas. The 1-D/2-D coupled model was calibrated with the real rainfall events and applied to analyze the effect of climate change on urban stormwater inundation for the 30-year frequency of design rainfall calculated by RCP 4. of the IPCC RCPs. In a simplified inundation analysis based on 1-D/2-D coupled simulation, the small-scale urban flooding in the small and medium cities was rapidly propagated within two hours after the occurrence of a surcharge overflow. The flooding wave propagation was highly related to the flow interaction with topographical obstacles as road, and bottom elevation or slope.